import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

public class LimitDocumentFilter extends DocumentFilter {

    public final int limit;

    public LimitDocumentFilter(int limit) {
        if (limit <= 0) {
            throw new IllegalArgumentException("Limit can not be <= 0!");
        }
        this.limit = limit;
    }

    @Override
    public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
        int currentLength = fb.getDocument().getLength();
        int overLimit = (currentLength + text.length()) - limit - length;
        if (overLimit > 0) {
            text = text.substring(0, text.length() - overLimit);
        }
        if (text.length() >= 0) {
            super.replace(fb, offset, length, text, attrs);
        }
    }
}